You are describing basic personality differences that are likely to persist for a long time. Chances are, your older son will always be more dependent on interaction with his peers than your younger son will. But I think that time and circumstance will certainly remedy the situation for you. Once your older son goes to school, he will have more children to be around and to play with during recesses. And, when the older one goes to school, your younger one will have more opportunity to play alone.
I wouldn't make a major attempt to change the traits of either of them to any great extent. Perhaps you could remind your younger son that he won't have his older brother around to play with during the day much longer. If you can make him realize that, he may become more tolerant. And I would praise the older one for wanting to play with his little brother (brag on him and tell him that some big brothers consider their little brothers to be intolerable pests), but remind him of the young one's need for a little space.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.